The widespread installation and availability of broad band fiber optic transmission cables has made it possible to substantially increase transmission rates as well as the number of communications which may be transmitted simultaneously through a medium. As a result, there has been substantial interest in wavelength division multiplexing systems and techniques.
Wavelength switchable or multi-channel laser transmitters which can be used for wavelength division multiplexing are known. One such transmitter has been disclosed in an article entitled "Multi-channel Grating Cavity (MGC) Laser Transmitter for Wavelength Division Multiplexing Applications," Nyairo et al., IEE Proceedings, pg. 337, 138 No. 5 (1991).
Another transmitter which utilizes integrated semi-conductor Laser array is disclosed in Soole et al., "Multiple Array Grating Integrated Cavity (MAGIC) Laser--A New Semi-conductor Laser for WDM Applications".
Known transmitters using integrated external cavity arrays however usually share a common gain region. As a result of the common gain element or region, optical intermodulation or cross-talk between wavelengths simultaneously present in the transmitter become a significant design issue.
There continues to be a need for laser driven optical transmitters which provide for simultaneous operation of several elements of a laser diode array such that optical cross-talk or intermodulation effects are reduced to a minimum. Further, it would be desirable to be able to fabricate such transmitter units without substantially increasing manufacturing costs.
Additionally, known transmitters tend to be relatively inefficient with respect to the input power levels required to achieve satisfactory output power levels. It would be desirable to be able to increase available output power while at the same time decreasing required input power levels.
Further, transmitters used in wavelength division multiplexing schemes are required to faithfully reproduce the design wavelengths with a high degree of accuracy. It would therefore be desirable that any such transmitter be inherently highly reliable, from the point of view of wavelength stability, among the available wavelengths, as well as exhibit pure spectral density in the design wavelengths.
It is also desirable that tuning of the transmitter be as simple as possible.